The invention relates to thermoplastic molding materials of high molecular weight, thermoplastic, aromatic polycarbonates based on aromatic dihydroxy compounds.
High molecular weight, thermoplastic, aromatic polycarbonates are employed in numerous technical fields of application, because of their typical tough and elastic properties. A disadvantage is their poor mold release when injection-molded, which frequently results in relatively long cycle times. However, for economic and technical reasons, it is desirable to shorten the cycle times as far as possible so as to manufacture larger numbers of moldings per unit time on the injection molding machines. This can be achieved by mold release at higher temperatures. The objective is, therefore, to so modify the polycarbonate melt that the release of the molding from the wall of the mold takes place with low release forces and at high temperatures, without sticking of the solidified melt to the wall of the mold. Easy mold release at high temperatures is in particular also desired in the case of complicated moldings which are molded in molds with parts which cannot be cooled (for example, cross-webs, cores and the like). Undesired sticking of the moldings and damage of the molds on releasing the moldings (breakage of pins and the like), coupled with great losses of time, are frequently the consequence.
In the past, long-chain aliphatic carboxylic acid esters of monohydric and trihydric alcohols have been added to improve the mold release of aromatic polycarbonates, in accordance with DOS (German Published Specification) 2,064,095, DOS (German Published Specification) 2,220,185, U.S. Pat. No. 3,784,595 and U.S. Pat. No. 3,836,499. However, a disadvantage of these mold release agents is the deterioration in mechanical properties on prolonged heat exposure, as a result of which the aromatic polycarbonates which have been modified according to DOS (German Published Specification) 2,064,095, DOS (German Published Specification) 2,220,185, U.S. Pat. No. 3,784,595 and U.S. Pat. No. 3,836,499, so as to give easy mold release no longer satisfy certain technical requirements. A further disadvantage is the ready volatility of the fatty acid esters of glycerol, which particularly manifests itself as a disadvantage at the high temperature at which polycarbonate is processed.